Moment of inertia calculator
Calculate the moment of inertia (second moment of area) of any beam or profile section — Ix and Iy about the centroidal axes — straight from its dimensions. Pick a shape or import a DXF, and Dimviz integrates the section polygon exactly (Green's theorem) to give Ix, Iy plus section moduli, radii of gyration and weight. The moment of inertia governs deflection and buckling, so getting it right matters.
DXF (LWPOLYLINE/CIRCLE) · CSV/XLSX with X,Y columns (blank row = new loop). DWG → export as DXF first.
EL 23,000 MPa · Pultruded FRP (E-glass / polyester)
| Area | A | 3800 | mm² |
| Mass / metre | m | 7.220(4.852 lb/ft) | kg/m |
| 2nd moment | Ix | 2.293e+7 | mm⁴ |
| 2nd moment | Iy | 1.682e+6 | mm⁴ |
| Section mod. | Sx | 229267 | mm³ |
| Section mod. | Sy | 33633 | mm³ |
| Gyration | rx | 77.67 | mm |
| Gyration | ry | 21.04 | mm |
| Torsion | J | 126667 | mm⁴ |
| Published catalogue weight: 5.80 kg/m · computed Δ 24% | |||
Derived exactly from the section polygon (Green’s theorem). Fillets excluded (<2% effect). Verify against certified data before release.
What the moment of inertia tells you
The second moment of area (I) measures how a section resists bending — a taller I-beam has a much larger Ix because material sits far from the neutral axis. Deflection is inversely proportional to I, so doubling depth can quarter deflection. Dimviz reports Ix about the horizontal centroidal axis (strong axis) and Iy about the vertical, both exact for the geometry you enter.
Computed, not looked up
Instead of a table lookup for a nominal size, Dimviz computes I from your actual section — including non-standard walls and dimensions — so the number matches the part you're really specifying. Change a flange thickness and Ix updates live.
FAQ
How do you calculate moment of inertia?+
Integrate y² over the cross-section area about the centroidal axis. For a rectangle, Ix = b·h³/12. Dimviz does this exactly for any section via polygon integration, giving Ix and Iy.
What's the difference between Ix and Iy?+
Ix is the second moment about the horizontal centroidal axis (governs strong-axis bending); Iy is about the vertical axis (weak-axis). Both come from the same geometry.
Is it the same as section modulus?+
No — section modulus S = I / c, where c is the distance to the extreme fibre. Dimviz reports both I and S. See the section modulus calculator.